Dense plasma focus

A dense plasma focus (DPF) is a type of plasma generating system originally developed as a fusion power device starting in the early 1960s. The system demonstrated scaling laws that suggested it would not be useful in the commercial power role, and since the 1980s it has been used primarily as a fusion teaching system, and as a source of neutrons and X-rays. A dense plasma focus (DPF) is a type of plasma generating system originally developed as a fusion power device starting in the early 1960s. The system demonstrated scaling laws that suggested it would not be useful in the commercial power role, and since the 1980s it has been used primarily as a fusion teaching system, and as a source of neutrons and X-rays. The original concept was developed in 1954 by N.V. Filippov, who noticed the effect while working on early pinch machines in the USSR. A major research program on DPF was carried out in the USSR through the late 1950s, and continues to this day. A different version of the same basic concept was independently discovered in the US by J.W. Mather in the early 1960s. This version saw some development in the 1970s, and variations continue to be developed. The basic design derives from the z-pinch concept. Both the DPF and pinch use large electrical currents run through a gas to cause it to ionize into a plasma and then pinch down on itself to increase the density and temperature of the plasma. The DPF differs largely in form; most devices use two concentric cylinders and form the pinch at the end of the central cylinder. In contrast, z-pinch systems generally use a single cylinder, sometimes a torus, and pinch the plasma into the center. The plasma focus is similar to the high-intensity plasma gun device (HIPGD) (or just plasma gun), which ejects plasma in the form of a plasmoid, without pinching it. A comprehensive review of the dense plasma focus and its diverse applications has been made by Krishnan in 2012. Pinch-based devices are the earliest systems to be seriously developed for fusion research, starting with very small machines built in London in 1948. These normally took one of two forms; linear pinch machines are straight tubes with electrodes at both ends to apply the current into the plasma, whereas toroidal pinch machines are donut-shaped machines with large magnets wrapped around them that supply the current via magnetic induction. In both types of machines, a large burst of current is applied to a dilute gas inside the tube. This current initially ionizes the gas into a plasma. Once the ionization is complete, which occurs in microseconds, the plasma begins to conduct a current. Due to the Lorentz force, this current creates a magnetic field that causes the plasma to 'pinch' itself down into a filament, similar to a lightning bolt. This process increases the density of the plasma very rapidly, causing its temperature to increase.